Hi Thierry, On 24.09.2020 12:16, Thierry Reding wrote: > On Thu, Sep 24, 2020 at 10:46:46AM +0200, Marek Szyprowski wrote: >> On 24.09.2020 10:28, Joerg Roedel wrote: >>> On Wed, Sep 23, 2020 at 08:48:26AM +0200, Marek Szyprowski wrote: >>>> It allows to remap given buffer at the specific IOVA address, although >>>> it doesn't guarantee that those specific addresses won't be later used >>>> by the IOVA allocator. Probably it would make sense to add an API for >>>> generic IOMMU-DMA framework to mark the given IOVA range as >>>> reserved/unused to protect them. >>> There is an API for that, the IOMMU driver can return IOVA reserved >>> regions per device and the IOMMU core code will take care of mapping >>> these regions and reserving them in the IOVA allocator, so that >>> DMA-IOMMU code will not use it for allocations. >>> >>> Have a look at the iommu_ops->get_resv_regions() and >>> iommu_ops->put_resv_regions(). >> I know about the reserved regions IOMMU API, but the main problem here, >> in case of Exynos, is that those reserved regions won't be created by >> the IOMMU driver but by the IOMMU client device. It is just a result how >> the media drivers manages their IOVA space. They simply have to load >> firmware at the IOVA address lower than the any address of the used >> buffers. > I've been working on adding a way to automatically add direct mappings > using reserved-memory regions parsed from device tree, see: > > https://lore.kernel.org/lkml/20200904130000.691933-1-thierry.reding@xxxxxxxxx/ > > Perhaps this can be of use? With that you should be able to add a > reserved-memory region somewhere in the lower range that you need for > firmware images and have that automatically added as a direct mapping > so that it won't be reused later on for dynamic allocations. Frankly, using that would be even bigger hack than what I've proposed in my workaround. I see no point polluting DT with such artificial regions just to ensure specific IOVA space layout. I just looking for a nice way of reusing most of the IOMMU DMA-mapping code with a small addition of manual IOVA space management (just to remap the firmware buffer at the specific IOVA address). Best regards -- Marek Szyprowski, PhD Samsung R&D Institute Poland
